Sail Area-Displacement ratio

The Sail Area-Displacement ratio (SA/D) is a calculation used to express how much sail a boat carries relative to its weight.[1]

${\displaystyle {\mathit {SA/D}}={\frac {{\mathit {SailArea}}({\text{ft}}^{2})}{[{\mathit {Displacement}}({\text{lb}})/64]^{\frac {2}{3}}}}={\frac {{\mathit {SailArea}}({\text{m}}^{2})}{{\mathit {Displacement}}({\text{t}})^{\frac {2}{3}}}}}$

It is an indicator of the performance of a boat.[2] The higher the SA/D, the more lively the boat's sailing performance:[3]

Boat Type	SA/D
Motorsailers	13 - 14
Slow auxiliary sailboats	14 - 15
Average offshore cruisers	15 - 16
Coastal cruisers	16 - 17
Racing yachts	17 - 19
Ultra light racers, class racers, daysailers	20+

SA/D, however, doesn't provide information about a boat behavior in a storm or upwind. A polar diagram from a velocity prediction program gives a more precise view.[4]

See also

• Displacement–length ratio

References

1. Paris, Jay E. "Comparing Design Ratios". Sail Magazine. Retrieved 9 July 2020.
2. McGeary, Jeremy. "How Sailboats Measure Up". Cruising World. Retrieved 9 July 2020.
3. Sponberg, Eric W. "The Design Ratios" (PDF). Sponberg Yacht Design Inc. Retrieved 9 July 2020.
4. Reisberg, Lars. "Sail Area-Displacement Ratio: Skipper´s Basics". No frills sailing. Retrieved 11 July 2020.